更多"________has been the major problem "的相关试题:
[单项选择]________has been the major problem in the Great Lakes in recent years.
A. Too many algae
B. Excessive recreational use
C. Lack of adequate rainfall
D. Too much evaporation
[单项选择]A great deal has been done to remedy the situation.
A. maintain
B. improve
C. preserve
D. protect
[填空题](No wonder) that (man’s) great dream has been someday to control the weather. The first step toward control is, of course, knowledge, and scientists have been (hard at work) for years trying to (keep track for) the weather.
A. No wonder B. man’s C. hard at work D. keep track
[单项选择]Over the last 40 years there has been a great increase not only in the number of agricultural pesticides in use but also in the care and sophistication with which they are used by farmers. Nevertheless, the proportion of agricultural crops lost to certain pests worldwide has increased over the same period, even when the pests concerned have not developed resistance to existing pesticides.
Which of the following, if true, best explains how improvements in pesticide use have been accompanied by greater losses to certain pests
A. Some dangerous but relatively ineffective pesticides common 40 years ago are no longer in widespread use.
B. As pesticides have become increasingly pest-specific, controlling certain pests with pesticides has turned out to cost more in many cases than the value of crop losses caused by those pests.
C. Because today’s pesticides typically have more specific application conditions than did pesticides in use 40 years ago, today’s farmers observe their fields more closely than did farmers 40 years ago.
D. Certain pest-control methods that some farmers use today do not involve the use of chemical pesticides but are just as effective in eliminating insect pests as those that do.
E. (E) Forty years ago, much less was known about the effects of pesticides on humans and other mammalian species than is now known.
[填空题]There has been a great increase in retail sales (零售), (has) ______ there
[单项选择]
The use of heat pumps has’ been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation. Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body or air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from th
A. explain the differences in the working of a heat pump when the outdoor temperature changes
B. contrast the heating and the cooling modes of heat pumps
C. describe heat pumps, their use, and factors affecting their use
D. advocate the more widespread use of heat pumps
[单项选择]How many times has the girl been to the Great Wall